Off-design performance of CAES systems with low-temperature thermal storage under optimized operation strategy

Compressed air energy storage (CAES) systems usually operate under off-design conditions due to load fluctuations, environmental factors, and performance characteristics of the system. However, the current research on off-design performance of CAES systems, especially in the aspects of advanced compressed air energy storage systems and operation strategies, is deeply insufficient. The complete off-design model of a compressed air energy storage system with thermal storage (TS-CAES) and optimal regulations by adjusting variable inlet guide vane (VIGV) and variable stator vane (VSV) is established for the first time. Using this model, we uncover the off-design characteristics common in TS-CAES systems caused by changes in load, ambient temperature, and operation type (constant pressure operation and sliding-pressure operation), and which is conducted under the optimal regulation strategy for the compression and expansion sections. It is found that system parameters fluctuate around a balance position with load fluctuation. But under the optimal operation, the fluctuation of the system efficiency and energy density is relatively small. System efficiency and energy density increase marginally with the decrease of ambient temperature, and thermal storage temperature increases linearly and markedly with rise in ambient temperature. We also found that system efficiency under constant pressure operation is decreased by 1.74 percent compared to that under sliding-pressure. This study will provide theoretical support for the design, operation, and control of TS-CAES systems.